The present invention relates to a rotary compressor, and in particular to, a swing type (piston swing type) rotary compressor that a swing piston is rotated orbitally within a cylinder chamber while a blade which is integrally provided with the swing piston being held by a cylinder and swung.
A swing compressor with a swing piston has been conventionally known as a rotary compressor as is disclosed in, for example, Japanese Patent Application Laid-Open (JP-A) No. 9-88852. The swing compressor is usually used in order to compress a gas refrigerant in a refrigerant circuit for a refrigerating machine.
In general, a swing compressor is structured so that its compression mechanism has a schematic horizontal sectional structure as shown in FIG. 8. A compression mechanism (100) comprises a cylinder (102) confining a cylinder chamber (101), a drive shaft (103) disposed so as to penetrate the cylinder chamber (101) and a swing piston (104) which is fitted into an eccentric shaft portion (103a) of the drive shaft (103) and thus accommodated within the cylinder chamber (101). The cylinder chamber (101) is formed so as to have a circular cross-sectional configuration. The drive shaft (103) is disposed concentrically with the cylinder chamber (101). The center of the eccentric shaft portion (103a) is eccentric from the center of the cylinder chamber (101).
A blade (104a) is formed integrally with the swing piston (104). The blade (104a) is connected via a swing bush pair (105) to the cylinder. Specifically, the swing piston (104) is supported to a free swing about the center of axis of a bush hole (102a) with circular cross-sectional configuration by the blade (104a) being inserted into the bush hole (102a) together with the swing bush pair (105) with substantially semi-circular form with interposed between the pair of swing bushes (105).
Further, the blade (104a) is supported so as to advance and retreat with respect to the bush pair (105) in the direction of its surface (i.e., in the radial direction of the swing piston (104)). The swing piston (104) is fitted in a free sliding into the eccentric shaft portion (103a) and rotated orbitally along the inner peripheral surface of the cylinder (102) without rotating on its own axis by rotation of the eccentric shaft portion (103a).
The cylinder chamber (101) is divided, by the swing piston (104) and the blade (104a), into a suction chamber (106) into which a refrigerant with low pressure is suctioned and a compression chamber (107) for compressing a suctioned refrigerant. A suction port (108) communicating with the suction chamber (106) and a discharge port (109) communicating with the compression chamber (107) are formed in the cylinder (102). A discharge valve (110) is attached to the exit of the discharge port (109). The discharge valve (110) is opened when a discharge pressure within the compression chamber (107) reaches a predetermined level.
In accordance with the swing compressor with the above-described structure, by the eccentric shaft portion (103a) being rotated, the swing piston (104) is rotated orbitally within the cylinder chamber (101) while the blade (104a) is swung, and thus a gas refrigerant suctioned into the cylinder chamber (101) is compressed and discharged by the cylinder chamber volume being varied. Specifically, in accordance with the swing compressor, when a pressure within the cylinder chamber (101) reaches a discharge pressure by a compression cycle performed in the first phase of the orbital movement of the swing piston (104), the differential pressure between inside the cylinder chamber (101) and outside the same reaches a predetermined value, so that the discharge valve (110) is opened. Then, a discharge cycle starts and the refrigerant is discharged.
A conventional swing compressor has the problem that an overcompression loss for a refrigerant becomes relatively large and thus a compression efficiency is decreased. Causes for this problem are as follows. Namely, in accordance with a conventional swing compressor, the position of the swing piston (104) when the discharge valve (110) is opened is usually positioned slightly over a bottom dead center as illustrated in an imaginary line shown in FIG. 8. The discharge cycle is performed in a relatively narrow angular range from this position to a vicinity of top dead center. Namely, in accordance with a conventional swing compressor, because of this relatively narrow angular range, the discharge cycle is performed in a short time and thus the flow rate of the discharged gas is increased. As a peak pressure is increased, an over compression loss for a refrigerant becomes large. As a result, the efficiency of compressor is decreased.
The present invention was developed in light of such problems and an object of the present invention is to reduce an overcompression loss generated when a refrigerant is discharged in a swing compressor and thus to prevent a decrease in efficiency.